[SOLVED] How to reuse console used by current process

How to reuse console used by current process

I want the following assembly to write Hello World! in the current console. Currently it is working but writes Hello World! into a new console window. I have tried removing the invoke AllocConsole statement but it does not write anything and exits with code -1073741819. What is the simplest way to use the existing console window when the executable is called from the terminal?

include 'win64ax.inc'

.data
    tex     TCHAR   'Hello World!'
    dummy   rd      1

.code
    start:
        ; Don't want to allocate new console. How to use existing??
        invoke  AllocConsole
        invoke  WriteConsole, <invoke GetStdHandle, STD_OUTPUT_HANDLE>, tex, 12, dummy, 0
        invoke  Sleep, 1000

.end start

Solution

Are you trying to make a console app instead of a GUI app? Then just define format PE64 console at the top of the file (instead of the format PE64 GUI which win64ax.inc defaults to). With this, you can just remove the call to AllocConsole, because a console app automatically gets allocated a console by the operating system, or the console from the parent process if that is a console process.

-1073741819 is NTSTATUS 0xC0000005 STATUS_ACCESS_VIOLATION, which you get because your function does not return (ret) or call ExitProcess. Note that .code inserts a sub rsp, 8 to align the stack, so you need to insert add rsp, 8 before the return of start to balance this out. Lastly, if you use ret, you may want to set the exit code in rax to 0.

Full code:

format PE64 console
include 'win64ax.inc'

.data
    tex     TCHAR   'Hello World!'

.code
    start:
        invoke  WriteConsole, <invoke GetStdHandle, STD_OUTPUT_HANDLE>, tex, 12, NULL, NULL
        xor eax,eax
        add rsp, 8
        ret

.end start

Result:

> .\print.exe
Hello World!